It is known to arrange the chucking cylinder of hydraulically drivable chucking devices in hobbing machines at the lower end of the workpiece spindle. This type of construction makes it necessary that the lower area of the spindle end must be accessible for installation and service which requires large windows or open spaces in the machine frame which weaken the machine frame.
It is also known to arrange the chucking cylinder in the area of the upper end of the workpiece spindle, for example on the spindle nose or face plate. However, the plane surface is interrupted by the mounting for the workpiece. Also in this type of construction, the pressure medium is fed to the chucking cylinder so that windows or spaces are needed in the machine frame for installation and service.
The basic purpose of the invention is to provide a hydraulic drive mechanism of the above described type in which, on the one hand, an all around closed machine frame is possible and, on the other hand, the mounting table on the spindle nose or face plate is not hindered.
In the below described exemplary embodiment, the small diameter connecting piece does extend between the chucking piston and the not shown chucking device beyond the gripping or mounting surface of the face plate, which is, however, not damaging, because at any rate a connecting element must move to the chucking device through the face plate and furthermore it is possible -- as can be taken from the drawing of the exemplary embodiment -- to design the connecting piece or the spindle nose (face plate) so that the connecting piece does not extend beyond the plane surface.
The invention makes it possible to release the chucking cylinder from the spindle nose from above and to draw them together with a pressure medium supplied by hose members hoses extending upwardly out of the workpiece spindle (during a servicing). During installation, the free ends of the hoses, which are connected to the supply system are pulled out upwardly through the workpiece spindle and are there connected to the pressure medium supply member and the thus completed device is then lowered from above into the workpiece spindle and is secured in place. It is obvious that this type of installation is more convenient and less time-consuming than an installation from below through windows and spaces in the machine frame. The pressure medium supply system itself can be erected outside of the machine frame; only the hoses or the like enter -- advantageously by means of threaded connections from outside into the inside of the machine frame and the hoses are so long on the inside that the drive mechanism according to the invention can be pulled out upwardly from the workpiece spindle.